(1) Field of the Invention
The present invention relates to a rights management terminal, a server apparatus and a usage information collection system, and in particular, to a technique of collecting usage information (e.g. a usage history of a digital content used by a terminal apparatus) that is anonymously sent, while preventing spoofing.
(2) Description of the Related Art
Recently, content distribution services under which a server apparatus (hereinafter to be referred to as “server”) distributes a digital content (hereinafter to be referred to as “content”) such as movie and music to a terminal apparatus (hereinafter to be referred to as “terminal” or “rights management terminal”) by which the content is used have entered a phase of practical application. The development of digital devices has made it easier to enact an unauthorized copy of a content, which causes an increase in the number of problems that a copyright of the content is infringed. This is why a technique of Digital Rights Management (DRM) is used in the content distribution system in order to prevent an unauthorized use of a content. The DRM is a technique for providing a secure license only to an authorized user or terminal apparatus, and authorizing a use of a content under the usage rules indicated in the license. The DRM applies an authentication technique or an encryption technique that uses the following: a public key certificate (hereinafter to be referred to as “normal certificate”) that includes identification information for uniquely identifying at least one of a terminal and a user who uses the terminal; and a private key paired with a public key included in the public key certificate.
According to the Japanese Laid-Open Patent Application No. 2002-522995, an example of a usage history collection system, in which a usage history of a content used by a terminal apparatus is previously stored and the usage history is regularly transmitted to a server apparatus, with the view to conduct a rating survey for each of the contents distributed as a content distribution service, is illustrated.
In order that the server apparatus may properly conduct a rating survey, it is required that the server apparatus accepts only usage histories sent by authorized terminal apparatuses and excludes those sent by unauthorized terminal apparatuses such as an apparatus that attempts spoofing. This can be solved, as in the case of distributing a license to a terminal apparatus, by receiving a usage history after verifying a validity of the terminal apparatus from which the usage history is to be transmitted, using the authentication technique with the use of normal certificate.
However, receiving a usage history after the terminal authentication may cause a problem of privacy since identification information is revealed based on a normal certificate and the terminal or the user can be identified.
Such problem can be caused not only in the case of collecting usage histories but also in the case of collecting usage information in general, regarding user's content usage, such as questionnaires inquiring about usage of content.